Cultural Management

Cultural control of the wheat stem sawfly has not been particularly effective (Morrill 1992). The primary cultural management strategy that has been attempted on the wheat stem sawfly is fall tillage. Secondary methods include swathing the wheat prior to cutting, crop rotation, and delayed planting in spring wheat.

Fall tillage of wheat stubble has not been shown to reduce sawfly infestation in following years (Morrill 1992), although tillage has been shown to cause higher levels of over-winter mortality (Morrill et al. 1993). Tillage may also have a negative effect on parasitoids, as the parasitoids tend to over winter higher in wheat straw rather than at the base of the stubble like the sawflies (Morrill et al. 1998). Wheat stem sawflies may escape tillage because most implements do not sufficiently break up the clumps of soil found around wheat stubble. Also it has been estimated that a single female sawfly will generally infest ten wheat stems during her adult life, with the result that it takes only one of ten survivors of the previous years infested stems to maintain a stable population.

Swathing and crop rotation also have their respective problems. Swathing requires the use of extra equipment (a swather or swather attachment) in order to cut the wheat. Damage may result to the combine used to harvest the swathed stems, as the bar must be set at a lower level. Also, while swathing may reduce the number of heads left behind by sawfly cutting, yield is still lost in heads from sawfly infested stems (Holmes 1977) and swathing may not kill sawflies that have already moved to the basal portion of the stems. Crop rotation can be effective as long as neighboring fields are not planted to susceptible crops (i.e. wheat or CRP grasses) (Criddle 1922). Later planting dates of spring wheat may also prevent sawfly infestation through breaking synchrony of the host and pests phenology (Morrill and Kushnak 1999).

 

Chemical Management

The wheat stem sawfly is difficult to chemically manage as the adults emerge and lay eggs over a three-week period and the larvae feed within the wheat stem beyond the reach of contact or stomach poisons. As a result, there are no registered insecticides for application on the wheat stem sawfly. Management strategies are therefore limited to cultural methods, biological control, and resistant plant varieties (Weiss and Morrill, 1992, Morrill 1995).

 

The Wheat Stem Sawfly Research Project conducts ongoing research to evaluate the effects of agricultural practice on the sawfly and its natural enemies. Comparison criteria consist of either block versus strip style planting, solid versus hollow stemmed wheat varieties, and tilled versus chem-fallow practices. Samples for this project have come from Montana wheat fields with pair-wise comparisons made between adjacent fields demonstrating one of the predetermined criteria for comparison.

Samples are collected in fields throughout the state and brought back to the lab. The stems collected are painstakingly dissected to determine sawfly and parasitoid infestation. Other data collected include: yield, seed count, stem height, and stem diameter. Data are then evaluated in order to better understand the dynamics of sawfly impact. These studies will help determine which agricultural practices best discourage the sawfly and encourage its natural enemies.